(a) Field of the Invention
The present invention relates to armatures for electrical rotary machines and more particularly to a cylindrical coreless armature and a process for producing coils for the same.
(B) Description of the Prior Art
A conventional example of a coil unit for a cylindrical coreless armature adapted to an electrical rotary machine provided with a stator having two magnetic poles is shown in FIGS. 1A and 1B. In this conventional example, the coil unit is formed as follows by temporarily providing a cylinder. A lead wire to form the coil first starts at one point on the peripheral edge of the cylinder, extends diagonally upward on the outer peripheral surface, becomes diagonally downward in a position separated by an electric angle of about 180.degree. along the periphery from the above mentioned starting point and comes to be adjacent to the starting point in a position of an electric angle of about 360.degree. to form one turn of the coil. This turn is repeated until the width of the coil unit formed of the lead wire becomes to be of a predetermined value so that one coil unit is formed. The effective length to the actual length of the lead wire can be taken to be so large that this conventional example can be said to be in a coil form high in the rate of utilization of the lead wire.
However, it is very difficult to form a coil unit as mentioned above. In fact, as shown in FIG. 2A, such coil unit as in FIG. 2B is made by a process wherein a lead wire is wound to be in the form of a solenoid and the solenoid is folded back in reverse directions along diagonal fold lines A and B in two positions and a plurality of such coil units are combined to make a cylindrical armature coil. Therefore, in the producing step, particularly the operation of folding back the assembly of the lead wire wound to be in the form of a solenoid is so difficult and the finish fluctuates so much that no uniform coil unit has been always obtained.
Further, the lead wire is wound to be in the form of a solenoid and the solenoid is folded back to be a coil unit. When the lead wire is in the form of a solenoid and when it is finished as a desired coil unit, the front and rear of one portion will be reversed respectively to those of the other portion with each fold line as a boundary. Therefore, a coil of many layers can not be made at once. In order to make a coil unit for many layers, there has been a complicacy that some coil units of one layer different in the diameter are made in advance and must be overlapped.
FIGS. 3 and 4 respectively show two different conventional examples of cylindrical coreless armatures formed by using many coil units made as mentioned above. According to the example in FIG. 3, the armature comprises an armature coil 1 made by cylindrically combining a plurality of coil units and then integrally securing them with a proper binder, a bracket 2 made of such electrically insulating material as a synthetic resin and secured to one open end of the cylindrical armature coil 1 and a rectifier 3 and main shaft 4 secured to the bracket 2. Further, according to the conventional example in FIG. 4, a tape T is wound on the outer peripheral surface of the armature coil 1. Usually, the armature 3 in FIG. 3 is made by bonding the armature coil 1 to the bracket 2 formed integrally with the rectifier 3 or by forming the bracket 2 by holding the relative positions of the armature coil 1 and rectifier 3 in a predetermined state as they are and filling them with a synthetic resin. According to such producing process, generally a binder having a strong bonding force is hard to obtain or the securing force of the resin to the armature coil is so small that the bracket is likely to collapse. There is a defect that, if the area of jointing the resin portion with the armature coil is taken to be wide or such reinforcing tape as in FIG. 4 is used to eliminate such defect, the contour of the entire armature will become larger and the rotary machine itself will have to be larger. Further, there is also a defect that it is difficult to maintain the precision of fitting the armature coil 1 to the main shaft 4.